Building codes and standards provide strict functional requirements for in-building emergency exit signage. Under existing standards, an exit sign must be provided at each exterior building exit and at each interior building exit (i.e., an exit from an interior building space to a stairway or hallway connecting to an exterior exit), and must be provided such that an exit sign indicating an exit, or the direction toward an exit, can be seen from anywhere in an interior hallway. Additionally, standards require that building exit signs be illuminated, which illumination must be maintained in the event of a power outage or other emergency such as a fire or flood. Certain exit signs have additional functionality, such as strobes or integrated lamps to illuminate the area around the sign and the exit door. Conventionally, exit signs are powered through a connection to a building's standard AC power service, and conventional systems can include backup batteries for maintaining illumination under power down or other emergency conditions.
FIG. 1 illustrates a conventional arrangement for providing illuminated exit signs or emergency luminaires. In the conventional arrangement, an AC power line is connected to a distribution panel for mains AC power, which in North America is typically 120, 240 or 277 VAC, 60 Hz. Connected across this line are one or more illuminated exit signs or emergency lights (hereinafter, “fixtures”). Not illustrated in FIG. 1 are the internal components of the individual fixtures, which may include lighting ballasts and fluorescent lamps and additional ballasts and lamps for the auxiliary strobes or spotlights described above. In the event that the fixture includes LED lamps, the sign will include rectifying and filtering electronics to convert the incoming AC power to DC and LED drivers or controllers to run the individual LED illuminators. Per code, building exit signs and emergency lights must be kept illuminated in the event of a power down condition, so some fixtures will include back up batteries, along with charging electronics and electronics to manage the switch-over to the battery. In other installations, backup power may be provided upstream of the fixtures, with a backup battery near the connection to mains.
The promulgation of IEEE standards for power-over-Ethernet (“PoE”), combined with the ubiquity of RJ45 Ethernet cabling in modern business and residential buildings, provides alternative means for building lighting, including the illumination and powering of emergency exit signs and emergency lighting fixtures. There are at present three ratified IEEE standards for PoE: IEEE 802.3af, IEEE 802.3at, and IEEE 802.3bt. An Ethernet port operating in accordance with the IEEE 802.3af standard is capable of supplying 12.95 Watts to powered devices (“PDs”) over a PoE link. IEEE 802.3at defines the PoE+ standard, which enables the delivery of up to 25.5 W over a PoE link. Currently, more advanced methods of this PoE standard provides up to 60 Watts (e.g., PoE+ and PoE++). The PoE standard IEEE 802.3bt specifies equipment capable of supplying up to 90 W over a PoE link.
Realizing a PoE link over the physical connections of Cat5+ Ethernet cable is done according to one of two alternatives, illustrated schematically in FIG. 2. As can be seen in FIG. 2, an RJ45 Ethernet cable 205 carries eight conductors grouped as four twisted pairs (210a,b and 215a,b), with two twisted pairs (e.g., 210, 215) forming a communication link for a first port (transmit and receive), and with the two remaining twisted pairs available as spares (e.g., 215a,b). In Alternative A, a DC voltage is supplied over data lines, across center taps on internal signal coupling transformers (220 a,b) connected across the pair of conductors on each of the transmit and receive twisted pairs. The DC voltage is then supplied from the center taps of another pair of transformers (225a,b) across the receive-side twisted pairs for the transmit and receive lines. This DC voltage is supplied to a powered device 230 on the receive end of the link. In Alternative B of the PoE standard, DC voltage is supplied through the unused or spare twisted pairs. Newer and proposed PoE standards provide more power and faster data using all 8 conductors. These methods require 4 data transformers, where power is imposed on all pairs.
A PoE network is arranged in a Point-to-Point topology, referred to as a “star” configuration. The standard Ethernet star topology, compared to other topologies, reduces the impact of node failures and provides isolation of errors so that the rest of the network will be unaffected, while maintaining communication speeds. PoE was introduced in 2003 and utilized the existing, mature and highly developed Ethernet with its star topology. PoE is a system where power and data are transmitted together over one cable. The transmitted power and data are intended for one single termination at each end of the cable (i.e., one ink segment). The power and data of one PoE port link segment are for use between one port from the PSE and one PD with a local IP address at the PD. The power capability of one PoE port link segment is significant, currently supporting 60 Watts, with future power levels planned to approach 90 Watts. Additionally, the digital communications speed capability of one PoE Port Link Segment is currently 1 Gb/s and approaching 10 Gb/s for future standards-based systems. Therefore, a one-to-one match in capability, both in terms of power and digital data communications, between the PoE Port link segment and the PD is helpful for full utilization of each port to be practical.
In recent years, with the declining cost and increased efficiency of light emitting diodes (“LEDs”), LED lighting has begun to replace fluorescent and incandescent lighting in commercial settings. FIG. 3 is a schematic representation of a conventional LED lighting installation powered by a PoE link, or more precisely, an Ethernet cable referred to under the PoE standards as a Port Data Link Segment. 48V DC nominal is supplied over the link by power sourcing equipment (“PSE”) 305 (e.g., a PoE switch, hub or midspan injector). The power is superimposed on data transmission wire pairs of an Ethernet link segment 310 (e.g., 310a, b) carried on a CATnx (e.g., CAT5e) cable. The link segments (310a,b) supply power to a Powered Device (“PD”), for example, PoE luminaire Lighting LED Driver 320, where the power is intelligently extracted (i.e., separated from the data) at the PD. Power extraction occurs at a PoE Lighting LED Driver 320, which appears to the PSE as any conventional PD operating according to the PoE standards. Power is then delivered by the driver 320 to LED lamps 325. In certain conventional implementations, driver 320 and LED lamps 325 are co-located in an LED luminaire 315, which is installed, for example at an illuminated exit sign.
Digital communications standards have been developed that permit the digital control of building lighting fixtures. One such standard is the Digital Addressable Lighting Interface standard, IEC 62838 (hereinafter “the DALI standard” or “DALI”) promulgated by the International Electrotechnical Commission (“IEC”). The DALI standard is available for purchase through the IEC at 3, rue de Varembé, 1st floor, P.O. Box 131, CH—1211 Geneva 20—Switzerland or by calling 41 22 919 02 11 and through the IEC's webstore at webstore.iec.ch. The DALI standard is incorporated by reference herein as though set forth in its entirety.
Under the DALI standard, a lighting controller (a host controller) including a digital transceiver sends digital commands to one or more connected luminaires via a bidirectional bus. These commands are received by a luminaire transceiver and executed by an associated microprocessor (a client controller) in communication with a ballast controller and a lamp. DALI commands are conventionally 16 bits long, and composed of an address byte (either an address of a single luminaire, or a group address for a group of luminaires) followed by a data byte, which causes the DALI receiver to execute one or more commands. Exemplary commands include setting the luminaire or executing one or more preset lighting scenes. The DALI standard also supports commands indicating lamp status, a power failure condition, a lamp or lamp component failure condition, etc. The DALI data communications rate is specified as 1200 baud, which is relatively slow by today's digital communications standards.
Topologically, multiple DALI devices receive and send commands to and from the DALI controller over a two wire data bus. According to the DALI standard, this control bus may also supply ≤250 mA at 16 V DC, allowing each device to draw 2 mA, which is typically sufficient to power the on-luminaire transceiver and control electronics. Power for the lighting ballast is typically supplied by building mains power (i.e., 120V AC). In certain installations of DALI connected luminaires, the DALI wiring has 4 or 5 conductors: two conductors for the data bus, and 2 or 3 for AC power (e.g., line, neutral and ground).